Francis Turbine Runner — Typical Number of Blades In a Francis turbine, the runner generally has how many blades?

Introduction:
Runner blade count influences flow guidance, hydraulic losses, cavitation behavior, and structural integrity in reaction turbines. Francis turbines, which operate at medium heads, adopt a blade count that balances efficiency and manufacturability.

Given Data / Assumptions:

• Francis runner with stay and guide vanes directing flow to runner blades.
• Standard industrial designs for medium specific speeds.

Concept / Approach:
Practical designs commonly employ several dozen blades for smooth guidance and to limit relative eddies. Too few blades increase incidence losses; too many raise surface friction and cost. The usual design window is approximately 16 to 24 blades for typical Francis turbines.

Step-by-Step Solution:
Assess flow guidance needs at part and full load.Select blade count to manage incidence and secondary flows.Adopt the widely used range 16–24 for general-purpose Francis runners.

Verification / Alternative check:
Manufacturer catalogues and design texts cite blade numbers in this range for standard sizes.

Why Other Options Are Wrong:
2–4 and 4–8: far too few for proper reaction guidance.8–16: lower bound is used in some high-specific-speed or special designs but typical mainstream range is higher.

Common Pitfalls:
Assuming blade counts similar to Pelton buckets or Kaplan blades; each turbine family differs.

Final Answer:
16 to 24